Manufacture of fiber articles



Patented Sept. 10, 1935 UNITED s'm'rss MANUFACTURE OF FIBER- ARTICLESGeorge A. Richter, Berlin, N. 11., assignor to Brown Company, Berlin, N.H., a corporation of Maine No Drawing. Application December 10, 1932,Serial No. 646,741

, -Claims.

This invention relates to the manufacture of I or free condition.Otherwise, the hydrated or gelatinized cellulose tends to bind togetherthe pulp fibers of the article into which the pulp is formed and,although enhancing the strength, tear resistance and other physicalqualities of the article, detracts from'its absorptive capacity, i. e.,from the amount of impregnant which the article takes up and from thespeed and uniformity with which the impregnant diffuses into andthroughout the article. Moreover, despite the fact that a fiber articlemay be possessed of good strength, tear resistance and other physicalqualities by virtue of the fact that its pulp component has beenhydrated or gelatinized, nevertheless, it has been established that itis those articles whose pulp component has been kept in a substantiallyunhydrated or free condition thatacquire the best physical qualitiesafter they have undergone impregnation with a given impregnant. Forinstance, water-laid felts made from cellulose .pulp which has beenpreserved in as free a condition. as possible, may be quite tender andlacking in tensile strangth, tear resistance, and other qualities tobegin with, but when they are impregnated with various binders such asasphalt, rubber and the like, they acquire remarkable toughness, body,strength, tear resistance, and other valuable physical properties.Again, they can imbibe quickly and unipaper-making type, e. g., afelt-forming machine.

In other words, the cellulosic stock must undergo mechanicalfiber-liberating or pulping action in the presence of water before itcan be satisfactorily formed into such articles as water-laid felts. Thesubjection of rags, rope stock or similar cellulosic material to beateraction, however, is inevitably accompanied by the hydration or gela- 6tinization of the pulp thereby prepared, wherefore, the conditioned pulpor halfstuff rather than being a free one, possesses a comparativelyhigh slowness and accordingly leads to felts of a relatively denseandboardy character. 1

In accordance with the present invention, a

- cellulose pulp or halfstufl' which has been hydratchemicals might beused for the purpose of destroying the hydrated or gelatinized cellulosepresent in the pulp, I prefer to use alkaline reagents of such a typeand under such conditions as will ensure the destruction of the hydratedor gelatinized cellulose without sensibly damaging 25 the pulp fibers.Indeed, by the selection of the appropriate alkaline compound andtreating conditions, it is possible to destroy the undesirablehydratedor. gelatinized cellulose while at the same time improving thepulp fibers for formation into water-laid felts or other fiber articlesdesigned to undergo an impregnating treatment. Thus, the hydrated orgelatinized cellulose may be destroyed while enhancing the absorbencyand purity of the pulp fibers so that water-laid felts 35 made from thepulp lend themselves better to impregnation not only because they areessentially free from undesirable cellulosic binding or cementingingredients, but because the pulp fibers themselves are soft andabsorbent and so. contlgiglblte such qualities to the felts in whichthey There are various ways in which the principles of the presentinvention may be availed of and there are various kinds of cellulos'icmaterials to 5 which these principles may be applied to greater or lessadvantage. Inasmuch as rag stock constitutes a form of cellulose inconnection with which the present invention may, so far as I am nowaware, be practiced to greatest advantage, 5

I shall describe specifically the conditioning of rag stock inaccordance with my invention for the preparation of water-laid felts.Thus a rag stock such as is commonly used as raw material in themanufacture of roofing or floor-covering 55 felts, may-constitute mystarting material. If desired, the rags may be cut or shredded whilesubstantially dry into the smallest pieces or cloth fragmentseconomically producible in this way, thereby minimizing the work thatneed be done by the beater engine and hence the generation of hydratedor gelatinized cellulose during the beating operation. The rags in anormal or reduced condition may then bedelivered into a hollander orbeater engine together with suflicient water to ensure circulation andthe beater roll may be run in the usual cutting relationship with thebed-plate until the rags have been reduced to a pulp or halfstuff whichcan be formed into a felt which is satisfactory from the standpoint ofuniformity of texture and smoothness of surface. Inasmuch as theresulting pulp or halfstuff will normally be a dilute aqueous pulpsuspension, that is, have a fiber content of about 5% .or less, as doesthe usual beaten stock, it may be desirable to thicken or partiallydewater the beaten pulp before it undergoes the action of a chemicalwhich destroys in large measure or practically entirely its hydrated orgelatinized cellulose constituent. To this end, the beaten pulp may bedelivered 'to thickeners or other dewateringjnstrumentalities whichraise its fiber content to, say, about 10% or greater.

. The pulp thus thickened may then be treated with an alkali undersuitable conditions of alkalinity and temperature to effect the desiredchange in the properties of the pulp.

According to one procedure, the thickened pulp is boiled in dilutecaustic soda solution, say one of about 1% to 3% strength underatmospheric or superatmospheric pressure for about one to three hours,whereupon the pulp is washed free of alkaline liquor. The washed pulp ischaracterized by its high freeness and softness. According to a secondprocedure,the pulp may be treated at or below room temperatureconditions with a caustic soda solution of greater strength, say, one ofabout 5% to 8% soda concentration,

for about 30 minutes to 2 hours, and then washed.

In such case too, the hydrated cellulose is dissolved or destroyed andthe pulp fibers transformed into a soft, absorbent condition. Accord'ing to a third procedure, the pulp may be subjected to the action of acaustic soda solution of mercerizing activity at or below roomtemperature conditions. At about room temperature, 20 C., a solution ofabout 18% or greater strength has full mercerizing activity, butinasmuch as such activity exists to some extent in solutions of as lowas about 10% strength at room temperature, such latter solutions mayalso be considered for the purposes of my invention as havingmercerizing activity. At lower than room temperature, say at 5 C., or atC., solutions of lower causticity than 10% caustic soda strength arecharacterized by their ability to mercerize ce1lulose fiber and todestroy hydrated cellulose associated therewith. It is thus possible toemploy various conditions of causticity and temperaturebe separated fromthe pulp as in a countercurrent washer designed to effect washing of thepulp with minimum dilution of the liquor so that the separated liquormay be re-used in the treatwashing the stock free from the liquor, theexcess liquor may be separated without dilution as in a centrifuge,thickener, or other separating apparatus. A portion of the liquormaythus be recovered in an undiluted condition and be refreezing point, inwhich case mercerization may be effected with even more dilute causticsoda so* lution as in such case ice or water crystals separate out fromthe solution, in consequence of which the unfrozen or liquid portion ofthe solution becomes more ooncentrated in caustic'soda and functionsmore effectively as a mercerizing agent. In the event that the treatmentof the pulp is performed with a refrigerated or partially frozenmercerizingliquor, it is of decided advantage to separate out the excessrefrigerated liquor from the pulp so as to conserve it in a refrigeratedas well as undiluted condition for the treatment of other pulp. Should aportion of the mercerstance, the so-called white liquor of a kraft pulp50' The-alkaline liquor may, if desired, contain suit- 55 izing liquorbe frozen, it may be thawed out to permit a separation of as much liquoras possible from the pulp before the pulp is washed.

The alkaline liquor used for the purpose of the present invention mayhave its alkalinity furnished in whole or in part by alkalies other thancaustic soda. For instance, when the treatment of the pulp is performedmore particularly at elevated temperature, the liquor may have its 1alkalinity furnished by sodium sulphide,' sodium carbonate, lime, sodiumborate, sodium phosphate, sodium sulphite, or like salts, which undergo4o hydrolysis in water to yield an alkaline aqueous medium. Some ofthese salts, like the borates, phosphates, and. sulphites, may requirethe use of higher treating temperatures to give the same effect as thatattainable through the use of caustic soda, sodium sulphide and sodiumcarbonate at lower temperatures.- It is of course possible to usevarious combinations of alkalies or salts which give an alkaline aqueousmedium. For inmlll, which as is well known,- contains sodium sulphide aswell as caustic soda, may in some instances be advantageously employed,either under mercerizing or under non-mercerizing conditions.

able oxidants such as hypochlorite bleach, so-

.dium peroxide, hydrogen peroxide, permanganate, or the like,particularly when it is strongly alkaline or is used under mercerizingconditions.

An oxidant should not, however, be used in an alkaline liquor when areducing agent like'sodium sulphide is present therein. An alkaline*"liquor containing an oxidant is of 'valuemore particularly in connectionwith a colored pulp, as it makes possible partial or completedecolorization r of the pulp. The fact is that in some cases it, may beadvantageous to treat the rags or other starting material before theyundergo beater action or while they are undergoing beater action withoxidants such as chlorine, hypochlorite bleach, permanganate or thelike, and then to wash the'pulp before it is treated with an alkalineliquor containing, if desired, additional oxidant.

ment of other pulp. If desired, rather than Insome instances, the ragsmaybecookedinan alkaline liquor and/or chlorinated or bleached prior tobeating. In other instances, the beaten stock may be chlorinated orbleached and then treated with alkaline liquor, as hereinbeforedescribed, to destroy hydrated cellulose present therein; or the beatenstock may be treated with alkaline liquor, as hereinbefore described, todestroy hydrated cellulose present therein and then bleached. The stockis preferably washed between the bleaching and alkaline treatments. Itis of course possible to apply the foregoing chemical treatments inother combinations or sequences, but in each case, the principle ofdestroying hydrated cellulose generated during the beating operation isutilized, thereby increasing the freeness of the pulp or halfstufi afterthe beating operation. I may, however, state that it is preferable tocarry out such alkali treatment as is desired or necessary only afterthe beating operation so as to refine or purify the pulp at the sametime as its hydrated cellulose constituent is being destroyed. Thechlorinating or bleaching treatment may, however, advantageously beperformed on the raw rags, as such treatment tends to promote subsequentdisintegration in the beater engine, whereas an alkali treatment ofrefinement of the rags, as by cooking in alkaline liquors, works theother way, that is, tends to diminish ease of disintegration in thebeater engine. If desired, however, the chlorinating or bleachingtreatment maybe performed partly before beating and partly afterbeating; or it may be performed in entirety after the beating operation,whereupon the rag pulp may then have its hydrated cellulose ingredientdestroyed by the action of an alkaline liquor which may simultaneouslyserve to remove oxycellulose or other undesirable products formed duringbleaching and otherwise to refine or purify the pulp. As alreadyindicated, the rags may be preliminarily cut or shredded in a dry way tofacilitate subsequent chemical treatment as well as beating.

When pulp or halfstuif containing hydrated or gelatinized cellulose isprocessed in accordance with any one of the foregoing procedures of myinvention, it is rendered so free that when made into felts on the usualfelt-making machines, the felts are comparatively tender or lacking intensile strength and tear resistance and are high- 1y .porous, bibulous,soft and flexible. Notwithstanding the fact that such felts are thuspoor in their physical qualities as unimpregnated felts, they can beimpregnated quickly and uniformly with various binders such as latex,natural and synthetic resins, cellulose ester solutions, waxes, bitumen,or other'binders of a thermoplastic, water-dispersed or dissolvedvariety, to form impregnated products of a high binder content andcharacterized by a highly desirable combination of characteristics. Thefelt may, for example, be

bituminized to form a sheet which is highly pliant and practically proofagainst tear, especially the initiation of tear, and hence highlyvaltear resistance in a-bituminized sheet, for example, since it isquite likely that when a tearing stress is applied to the sheet, thestress rather than becoming localized and giving rise to rupture of thesheet, is not confined to any particular subjected to beater action.

locus, but it is distributed and/or dissipated over a large areaonaccount of the freedom of the fibers to slip or move past one another.

In making the water-laid felts or foundations of the present invention,it may be of advantage 5 to admix with the free pulp or halfstuff asuitable small proportion of pulp in a partially hydrated or wellhydrated condition. The well'hydrated pulp may be prepared by beatingrag stock as hereinbefore described or by over-beating such stock orother suitable cellulose fiber in much the same way as is done inconnection with the manufacture of glassine papers. The best kinds ofhydrated or gelatinized cellulose for blending with the free pulp orhalfstuff is-that prepared in aso-called stone-rolled beater from kraftor other wood pulps refined by alkali to higher alpha cel-' lulosecontent. In connection with pulps which have been rendered free by theuse'of caustic soda solutions of mercerizing activity, it is desirableto use a suitable proportion of unmercerized cellulose pulp which may bein a substantially unhydrated, partially hydrated or well hydratedcondition. The use of some unmercerized pulp together with themercerized pulp facilitates the production of uniformly textured felts,serving to offset the clumping or bunching tendencies in mercerizedpulp. It is, however, possible to avoid clumpy or non-uniformfeltformation even when the entire felt-making furnish is mercerized bydelivering the furnish in an extremely dilute and well mixed conditionto the felt-forming machine. The use of hot water as a suspending mediumfor the mercerized pulp also mitigates the clumping or bunchingtendencies of the mercerized fibers. It is to be observed that inaccordance with my invention, the beating of rags, rope stock or othersimilar cellulosic materials, which shall be designated in the appendedclaims by the generic expression "rag stock" and which must be reducedto fibers of the appropriate size for uniform felting on machinery ofthe paper-making type, is practiced in water containing little, if any,alkali. While it may be possible to inhibit the generation of hydratedor gelatinized cellulose by using a large amount of alkali in the waterin which beating is being effected, nevertheless, the presence ofconsiderable alkali in the beater water would interfere seriously withthe rate at which the rags or similar cellulosic material would offriction between the cutting edges of the beater roll and the fibrousmaterial.

I have observed, 60 for example, that it is much more difficult toreduce refined rag stock, for instance, rag stock which has beenmercerized, than unrefined rag stock into a pulp or halfstuff eventhough substantially all of the alkali has been removed from the refinedor mercerized rag stock before it is By adopting the practice of thepresent invention, it is possible to take advantage of the ease withwhich unrefined rag stock can be reduced to a pulp or halfstuif in thebeater engine and then to destroy through the use of a suitable chemicalreagent, preferably alkali, the undesirable constituents and moreespecially the hydrated or gelatinized cellulose present in theresulting pulp or halfstuff.

'without substantial subsequent beating of the fibers forming theresultant pulp with its fibers at essentially the same length as afterthe beating operation, into a waterlaid felt.

2. A process which comprises bleaching rag stock whose fibers must bereduced in size 'in order to be uniformly feltable, beating the bleachedrag stock in the presence of -water to form a hydrated, uniformlyfeltable 'pulp or halfstuff, thereafter treating the beaten pulp with analkaline liquor to destroy hydrated cellulose and thereby to increaseitsfreeness without sen sibly damaging the pulp fibers, washing thetreated pulp, and, without substantial subsequent beating of the fibers,forming the resultant pulp with its fibers at substantially the samelength as after the beating operation, into a waterlaid felt.

3. A process which comprises beating ray stock whose fibers must bereduced in size in order to be uniformly feltable, in the presence ofwater to form a hydrated, uniformly feltable pulp or halfstufi',bleaching the beaten pulp, thereafter treating the bleached pulp with analkaline liquor to destroy the hydrated cellulose and thereby toincrease its freeness without sensibly damaging the pulp fibers, washingthe treated pulp, and, without substantial subsequent beating of thefibers, forming the resultant pulp with its fibers at essentially thesame length as after the beating operation, into a waterlaid felt.

4. A process of producing a waterlaid felt which 5 comprises beating ragstock, whose fibers must be reduced in size in order to be uniformlyfeltable, in the presence of water to form a hydrated, substantiallyuniformly feltable pulp or halfstufi containing the fibers insubstantially their final felt-making size, thereafter treating the pulpwith an alkaline liquor to destroy hydrated cellulose and thereby toincrease .the freeness of the pulp without sensibly damaging the pulpfibers, washing the treated pulp, and, without hydrating 1'5 of the pulpthereafter, forming the resultant freer pulp, with its fibers atessentially the same length as after the beating operation, into awaterlaid felt.

5. A process of producing a waterlaid felt which comprises beating ragstock, whose fibers must be reduced in size in order to be uniformlyfeltable, in the presence of suflicient water to form-a hydrated,substantially uniformly feltable pulp or halfstuff of a fiber contentdownwards of about 5% and containing the fibers in substantially theirfinal felt-making size, thickening the hydrated pulp-to a fiber contentof at least about 10%, thereafter treating the thickened pulp with analkaline liquor to destroy hydrated cellulose and thereby to increasethe freeness of the pulp without sensibly damaging the pulp fibers,wash- .ing the treated pulp, and, without lwdration of the pulpthereafter, forming the resultant freer pulp, with its fibers atessentially the same length as after the beating operation, into awaterlaid felt. v

GEORGE A. RICHTER.

